Holistic SEO is when you take content marketing and social media into consideration, the idea is to expand your thought to creating influencer status within your space that means you take into consideration social media, not for direct SEO ranking, but as an element of the ecosystem, that then helps you gain a wider audience which in turn helps with SEO in terms of engagement metrics affecting RankBrain . Eric Enge deals with this in his advanced SEO course at
Coursera: https://www.coursera.org/learn/seo-tactics
Holistic SEO means looking at the bigger picture too, so technical SEO, on-page SEO (content marketing) and obviously off-page SEO. To get up to scratch read:https://www.brandseedseo.co.za/seo-cape-town-guide/